DINSRDC/SPD-1179-01 IONAL WAVE MEASUREMENTS DURING THE HR. MS. TYDEMAN SEA TRIAL VIN SIDE /OFO-1 LT - Ol DAVID W. TAYLOR NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER | Bethesda, Maryland 20084 DIRECTIONAL WAVE MEASUREMENTS DURING THE HB. MS. TYDEMAN SEA TRIAL by Robert J. Bachman and Edward W. Foley APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED SHIP PERFORMANCE DEPARTMENT DOCUMENT: LIBRARY Woods Hole Oceanographic December 1985 Institution DINSRDC/SPD-1179-01 MAJOR DTNSRDC ORGANIZATIONAL COMPONENTS DTNSRDC COMMANDER TECHNICAL Re crer OFFICER-IN-CHARGE OFFICER-IN-CHARGE CARDEROCK ANNAPOLIS SHIP SYSTEMS INTEGRATION DEPARTMENT 12 AVIATION AND SURFACE EFFECTS SHIP PERFORMANCE DEPARTMENT DEPARTMENT 15 COMPUTATION, MATHEMATICS AND STRUCTURES LOGISTICS DEFARIMENT DEPARTMENT PROPULSION AND AUXILIARY SYSTEMS SHIP ACOUSTICS DEPARTMENT DFPARTMENT i ? SHIP MATERIALS CENTRAL ENGINEERING z INSTRUMENTATION DEPARTMENT DEPARTMENT I ii ) IY OTN NDW-DTNSRDC 3960/43 (Rev. 2-% GPO 866 993 - UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE REPORT DOCUMENTATION PAGE 1b. RESTRICTIVE MARKINGS 3 DISTRIBUTION/ AVAILABILITY OF REPORT Ya. REPORT SECURITY CLASSIFICATION IFIED 2a. SECURITY CLASSIFICATION AUTHORITY 2b DECLASSIFICATION/ DOWNGRADING SCHEDULE APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED 4 PERFORMING ORGANIZATION REPORT NUMBER(S) 5 MONITORING ORGANIZATION REPORT NUMBER(S) DINSRDC/SPD-1179-01 6a. NAME OF PERFORMING ORGANIZATION 6b OFFICE SYMBOL | 7a NAME OF MONITORING ORGANIZATION David W. Taylor Naval Ship (If applicable) Research & Development Center | 1561 6c ADDRESS (City, State, and ZIP Code) 7b. ADDRESS (City, State, and ZIP Code) Bethesda, Maryland 20084-5000 183. NAME OF FUNDING/ SPONSORING 8b. OFFICE SYMBOL | 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER } ORGANIZATION (If applicable) - Naval Sea Systems Command Be ADDRESS (City, State, and ZIP Code) 10 SOURCE OF FUNDING NUMBERS PROGRAM PROJECT WORK UNIT ELEMENT NO NO ACCESSION NO Washington, D.C. 20362 62759N SF 59-557 |DN1780231 1) TITLE (Include Security Classification) DIR&CTIONAL WAVE MEASUREMENTS DURING THE HR. MS. TYDEMAN SEA TRIAL 12. PERSONAL AUTHOR(S) Robert J. Bachman and Edward W. Foley 13a TYPE OF REPORT 13b TIME COVERED 14 DATE OF REPORT (Year, Month, Day) 15 PAGE COUNT Final FROM _ iO | 1985 December 44 16 SUPPLEMENTARY NOTATION COSATI CODES GROUP SUB-GROUP 19 ABSTRACT (Continue on reverse if necessary and identify by block number) 18 SUBJECT TERMS (Continue on reverse if necessary and identify by block number) Directional Waves Wave Buoy Comparisons Trials were conducted in May 1982 aboard the Dutch oceanographic research ship Hr. Ms. TYDEMAN to compare the performance of three wave buoys. These were a disposable buoy designed and built by Delft University of Technology, a WAVEC buoy under development by the Datawell Corporation, and an ENDECO Corporation Wave-Track buoy owned by the David Taylor Naval Ship Research and Development Center. The disposable buoy provided energy spectra, | while the other two buoys provided energy spectra and wave directionalities. The time f histories of the significant wave heights and modal wave periods of the WAVEC and the Wave-Track buoys generally agree throughout the experiment. The energy spectra, mean wave directions, and spreading angles are also presented for most of the runs measured by the WAVEC and the Wave-Track buoys. The spectra of the two buoys are similar, with the WAVEC buoy showing higher peaks in a majority of cases. The mean directions basically compare well for wave frequencies above 0.11 hertz. Wave-Track mean directions below this range on _ reverse side 21. ABSTRACT SECURITY CLASSIFICATION 20 DISTRIBUTION / AVAILABILITY OF ABSTRACT CIUNCLASSIFIED/UNLIMITED &] SAME AS RPT Unclassified . 22a NAME OF RESPONSIBLE INDIVIDUAL 22b TELEPHONE (Include Area Code) | 22c. OFFICE SYMBOL Robert J. Bachman 202/227-181 Codemls61e DD FORM 1473, 84 MAR 83 APR edition may be used until exhausted SECURITY CLASSIFICATION OF THIS PAGE Alloth ditions are obsolete f Siva eee eT UNCLASSIFIED | (C1) otic USERS UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE Block 19 (continued) are often too sporadic for comparison with the WAVEC directions. The spreading of the Wave-Track directional energy is greater than the spreading of the WAVEC directional energy. The observed wave directions agree more favorably with the mean directions associated with the peak frequency of the Wave-Track buoy during the first half of the experiment and with those of the WAVEC buoy during the second half of the experiment. UNCLASSIFIED eee eee SECURITY CLASSIFICATION OF THIS PAGE TABLE OF ISU OW WIGWINHS 696 6 SSG 676) 6675" 6 6 WN 9 6 GG OO" GG To “Gols a" Ss 6y67'd INSSUIVNGM 6 GWGl OG 7G BMG 6 6 ola oNb6 ADMINISTRATIVE INFORMATION . ...e« « IOAN CO IDIUKCALILOIN, GG aOR BMG VoNG a6! GU6NG 66 TEN SLRUMEN ATT ON icy eve Veuice Usiiey el vel wey ie) fe. le MPROC/NILy- IDSC IRILIEARILOIN, 5G GSES IG GG oa! 66! 6 JNNIAINGSHES © Gi Gs 6 “SMG 6! 66S “SC Gls 6 SUS 6 IDVMIUA JRO INSISIUNGrG™G GOO lO “ONUMO Ol UOMO IDILSOUSISICOIN s 6G 6 MSN Nol BG 6! GaN SoG" 6 CONCLUDING REMARKS <« 2. 2's « © « » «© « « ACKNOWLEDGMENTS 2. . « © « © © «© © «© © @ « RETRENCHSs We elle) 6) es) © ©) 0) 6). ee) 0 0) 1m Datawelle WAVING: "BUOV) ja. (es) ie ol) 0 | 6) ie 2 oS Woilbtie Walsoeseiollig: lewis Go Goo oO ad Sa— otabullkizatitonmoty Deltat Buoy ss s/s 4 — ENDECO Type 956 Wave-Track Buoy ... LCD EMANRLrainiSHite ROUGE We) Weiliel le) inet Melitoible CONTENTS Page SSM Er BMS S SPS SVS SONG dive! “alta BS SOE SBS BN ESS S9 6 Vag |) sar 6 ONG 6 6"6.6 O00) Oo bi 6d 6-6 6 ml 6 6 O10 6 60 6 0 6 6 66 1 00 60 1 9 alo 606 OO Oo oO 06 6 6 16 NGG i 6 O66 OSG 6 ot ob 666: ote ol 3 OW Stas SaMBM SPR ONE a NS igi “SY ollis 4 S- 6TOVS"S 6 6.6 OGG 616 6 6 6 OM 5) 8.06 6 %0%6, 6 6 %6"5 6660 6 6 0! 6 a(t 6 86 “6 666 Silo O95 66S 6 6 G6 0 Bo aS Sl dio 16 69"6: 6 6 6 oo No Ul iG 12 SO Sal Glo) Gis Oo! 6 6 6 6 6 6 6 60 13 36) 6 6 6!) 6 6 od 6) G6 6 6 0 00 15 6 Jo ho 8 960 16.0 §o 0 G6 Ge ol 0b iif 15 OOO GO OO O10 BD Om oe Oro) 1G G ONG 6 66 616 6 6 4 6°96 O46 6 O10 19 6) 16" 6 oO Golo oO oo 6 SIG .6 6 6 6 O 20 COMO, LOOM OL oO Oa TO NON CMO Odo. oO 50 al 6 - Time History of Wind Speed, Direction, Measured Wave Directions and Observed Wave Direction 7 - Time History of Modal Wave Period and ° e e @ Wiley cen ea ce! eo e Oe Len ne e 8 22 Significant Wave Height . .... - 23} 8 - Energy Spectrum, Mean Wave Direction and Spreading of Runs 3 and 4 ... 24 9 - Energy Spectrum, Mean Wave Direction and Spreading of Runs 5 and Gi cueien ys 25 iii 10 all 12 AS} 14 15 16 aL ff 18 19 20 al 22 23 Energy Energy Inergy Energy Energy Energy Energy Energy Energy Energy Energy Energy : Energy Energy Spectrum, Spectrum, Spectrum, Spectrum, Spectrum, Spectrum, Spectrum, Spectrum, Spectrum, Spectrum, Spectrum, Spectrum, Spectrum, Spectrum, Mean Mean Mean Mean Mean Mean Mean Mean Mean Mean Mean Mean Mean Mean 1 -— Times and Locations of Wave Wave Wave Wave Wave Wave Wave Wave Wave Wave Wave Wave Wave Wave Data Direction Direction Direction Direction Direction Direction Direction Direction Direction Direction Direction Direction Direction Direction and and and and and and and and and and and and and and TABLE Collection . iv Spreading Spreading Spreading Spreading Spreading Spreading Spreading Spreading Spreading Spreading Spreading Spreading Spreading Spreading ee eo e @ of of of of of of of of of of of of of of Runs 7 and 8 . Runs 9 and 10 Runs Runs Runs Runs Runs Runs Runs Runs Runs Runs Runs 12 16 19 21 23 25 2T 30 32 3h 36 and and and and and and and and and 14 Ii 20 22 an 26 28 31 33 35 Page 26 27 28 2g 30 Sil 32 55 34 35 36 Sif 36 39 LO ABSTRACT Trials were conducted in May 1982 aboard the Dutch oceanographic research ship Hr. Ms. TYDEMAN to compare the performance of three wave buoys. These were a disposable buoy designed and built by Delft University of Technology, a WAVEC buoy under development by the Datawell Corporation, and an ENDECO Corporation Wave-Track buoy owned by the David Taylor Naval Ship Research and Development Center. The disposable buoy provided energy spectra, while the other two buoys provided energy spectra and wave directionalities. The time histories of the significant wave heights and modal wave periods of the WAVEC and the Wave-Track buoys generally agree throughout the experiment. The energy spectra, mean wave directions, and spreading angles are also presented for most of the runs measured by the WAVEC and the Wave-Track buoys. The spectra of the two buoys are similar, with the WAVEC buoy showing higher peaks in a majority of cases. The mean directions basically compare well for wave frequencies above 0.11 hertz. Wave-Track mean directions below this range are often too sporadic for comparison with the WAVEC directions. The spreading of the Wave-Track directional energy is greater than the spreading of the WAVEC directional energy. ‘The observed wave directions agree more favorably with the mean directions associated with the peak frequency of the Wave-Track buoy during the first half of the experi- ment and with those of the WAVEC buoy during the second half of the experiment. ADMINISTRATIVE INFORMATION The work reported herein was sponsored by the Naval Material Command/Naval Sea Systems Command Exploratory Development, Surface Wave Spectra for Ship Design Program (P.E. 62759N, SF 59-557). The work was carried out at David W. Taylor Naval Ship Research and Development Center (DINSRDC) under Work Unit Numbers 1500-382, 1500-383, 1500-384, and 1500-385. INTRODUCTION During the spring of 1982, a joint wave buoy study was conducted with partici- pants from the Netherlands and the United States. The scientific party consisted of members of the Delft University and the Datawell Corporation from the Netherlands and DINSRDC from the United States. Wave and wind data, along with ship motions were measured on board the Dutch research ship Hr. Ms. TYDEMAN while transiting the eastern North Atlantic. Wave data were measured using two direc- tional sensing wave buoys, which provided directional spectra, and an acceleration buoy, which provided point spectra. Datawell supplied a wave slope following buoy, referred to as the WAVEC buoy, and Delft University supplied a low cost, "disposable" acceleration buoy. DINSRDC supplied a wave orbital following buoy manufactured by ENDECO and designated as the Type 956 Wave-Track. Ship motion and wind were measured by the team from Delft University. This wave study provided an opportunity to compare the wave height and directional measuring capabilities of the Wave-Track buoy in relation to the other buoys and the observed data. The Wave-Track approach to directional wave measure— ment is based on a different concept to the conventional slope following method, i.e., the determination of wave directions by sensing the wave orbital velocities. This allows the design of the buoy to be small and lightweight compared to slope following buoys. For trials work, the Navy requires a lightweight, easy-—to-handle directional sensing wave buoy that provides a first order measurement of wave directionalities. The ENDECO Wave-Track Buoy gives the U.S. Navy a tool to help validate its spectral wave model. The Spectral Ocean Wave Model (SOWM), operational since 1975 at the Fleet Numerical Oceanography Center (FNoc)21* in Monterey, California, provided forecasts of wave environmental conditions at specified grid points in the Northern Hemisphere every 12 hours. The model permits the simultaneous represen- tation of both locally generated wind seas and swell from decaying or distant storms. The wave model can also be used in a hindcast mode by using historic pressure field data to derive wind and ultimately wave data. Some of the results have been reported in References 2 to 7. Within the past year a newer ocean wave model has been used, replacing the SOWM at FNOC. The Global Spectral Ocean Wave Model (GSOWM) provides forecasts of wave data with a finer grid spacing of 21/2 degrees. The new model still generates forecasts every 12 hours, but now encompasses both the Northern and Southern Hemispheres. In addition to its use with SOWM, the directional wave sensing capability of the Wave-Track buoy allows the Navy to apply the measured directional seaway to predicted ship response amplitude operators (RAOs). The developed ship responses can then be compared to trial measurements to help validate predicted RAO values. ¥A complete listing of references is given on page 15. Some wave height spectra from the above mentioned three buoys have already been presented by Foley, et a1.® and Gerritsma.? Foley, et alo indicated that for three different analysis techniques of data obtained from the Wave-Track buoy, the spectral shapes were quite similar, but the total energy varied. When the three different buoys were analyzed using a single technique, Gerritsma? indicated that the Wave-Track buoy measured a lower significant wave height in 22 of 35 runs com-— pared to the WAVEC buoy, the root mean square (RMS) of the differences being approximately 11 percent. This data, however, as analyzed by Delft University, did not have appropriate phase corrections applied to it. The application of the phases would tend to increase the resulting Wave-Track energy values. INSTRUMENTATION The instrumentation used during the TYDEMAN trial consisted of equipment supplied by Datawell Corporation, Delft University, and DTINSRDC. Each organiza- tion supplied a wave buoy, recording instrumentation, and a small computer for analysis. The Datawell Corporation supplied their new WAVEC buoy for the trial as shown by the photograph of Figure 1. The buoy was considerably larger and heavier than the other buoys although exact dimensions and weight are not known to the authors. The accelerometer, pitch-roll sensors, batteries, instrumentation and telemetry equipment were all housed within a container approximately the size of a standard 55 gallon drum. Attached to this drum was a specially constructed flotation collar which gives the buoy hull a discus shape. This slope following discus buoy has a spherically shaped dome structure to prevent capsizing. Delft University designed and supplied a "disposable" wave buoy for the trial. This buoy was designed to be of minimal cost and yet still be a reliable instrument for the measurement of ocean waves. The buoy is referred to as the Disposable Buoy or the Delft Buoy and is shown in Figure 2. The buoy sphere is a fiberglass construction and contains rechargeable batteries, a fixed vertical accelerometer, electronics, and an FM transmitter. The accelerometer signal is not double integrated onboard the buoy, as might be expected of a more expensive buoy. A buoy of essentially the same design is now available commercially under the trade name of "WADEL" and manufactured by the AVD Corporation in Rijswijk, Holland. Reference 10 describes the Delft buoy and its use, sometimes as a disposable instrument, during several sea trials. A complete description of the buoy is given in Reference 11. However, the basic hydrodynamic stabilization of the fixed vertical accelerometer can be understood from Figure 3. The rigid tripod tail of the buoy (length Ly) has a weight G attached to it by a wire rope of length Lo. A wave induced moment M would result in a buoy tilt of 8 degrees. In this condition, an erecting moment of Bay times L, would be obtained, where Fy is the perpendicular component of the wire tension to the tail. During this trial, a wire length of LO meters was used such that L5 can be assumed to be much greater than L, and thus the angle a approaches zero. Therefore, the erecting moment can be expressed as 135) © Ib SE Os Says} 2 dlsg) (a) This rather simple method for vertical stabilization of the accelerometer seemed to function very well with no tilting of the sensor observable. DINSRDC deployed an ENDECO Corporation Wave-Track Directional Buoy during the trial. This buoy is the result of development work at the University of Rhode Island as well as ENDECO Corporation and has been the subject of several papers. !2-14 The Wave-Track buoy was also deployed during the ARSLOE experiment as reported in Reference 15. The configuration of the buoy is shown in Figure 4. The sphere of the buoy (fiberglass) houses the electronics, transmitter, and batteries for the buoy, while the lower pendulum assembly (PVC and stainless steel hardware) houses the pitch-roll sensors, flux gate compass, and accelerometer. The pendulum assembly acts as a moment arm to tilt the buoy in response to the orbital motion of the incident wave field. This buoy has thus been classified as an orbital following buoy. Because of its inherently stable design the Wave-Track buoy is not subject to the capsizing problems associated with the discus slope following buoys. The signals from the buoys were recorded in analog form each using a Honeywell Model 5600 recorder. These recorders provided backup to the computer systems and digital recording of the data. Delft University and Datawell Corporation employed Hewlett-Packard microcomputer systems, while DTNSRDC used a Digital Equipment Corporation microcomputer system for the purpose of digital data collection and analysis. TRIAL DESCRIPTION TYDEMAN is a 90 meter open ocean research ship equipped with various cranes and winches necessary for general oceanographic research. The design of the ship and expertise of its crew made a relatively routine procedure of launching and recovering the wave buoys. The trial consisted of several buoy launches at nine locations along a transit from Den Helder, Netherlands to Santa Cruz de Tennerife in the Canary Islands, and the transit is shown in Figure 5. The route was deter- mined in part by daily wave forecasts received from FNOC. During the trial, the FNOC forecasts were examined approximately every 12 hours in order to identify regions of greater wave activity. When possible, the course of the ship was altered to steam towards those regions. A typical day's operations began with an early morning launch of the three wave buoys. The ship then conducted course keeping maneuvers to evaluate the seakeeping characteristics of the ship while the buoys free floated from the site of the launch. Near midday, the ship maneuvers were temporarily halted, and the buoys located, retrieved and then relaunched. This was necessary in order to keep the three buoys in a reasonable proximity to one another since they had varying drift rates. The WAVEC buoy had by far the highest drift rate due to the large sail area of the styrofoam cap. The Wave-Track and Delft buoys stayed closer together with the Wave-Track drifting slightly more than the Delft. After col- lecting data during the afternoon with the ship conducting maneuvers once again, the buoys were relocated and retrieved prior to darkness. Thus, wave data were collected in a nearly continuous fashion throughout the daylight hours. During the night, the ship transited and sometimes adjusted course to encounter more severe weather as located by the wave forecasts. ANALYSIS The technique DTINSRDC used to analyze the data is based on the Longuet-Higgins approach of calculating the first five Fourier coefficients. The Fourier coef- ficients are calculated from the coincident and quadrature spectra which in turn are determined from the auto spectra of each channel and cross spectra of the three channels, i.e., heave, north-south (n-s) slope, and east-west (e-w) slope. The coincident spectrum is proportional to the product of the magnitude and cosine of the phase of the cross spectrum, while the quadrature spectrum is proportional to the product of the magnitude and sine of the phase of the cross spectrum. When two measurements are 90 degrees out of phase, such as the heave and slope of a wave slope following buoy, they can be related by the quadrature spectrum, i.e., Qo When two measurements are in phase, such as the heave and slope of a wave orbital following buoy, they can be related by the coincident spectrum, i.e., Cio. Since the n-s and the e-w slopes of both the wave orbital following buoy and the wave slope following buoy are also in phase, they can be related by the coincident spectrum, i.e., Coz As expressed by Ewing and pittl®, the normalized Fourier coefficients can be determined from the following equations Ay = Cy (2a) a = Cyp/ Vey] (Cap + C33) (2) by = Cy3/¥q1 (Cop + C33) (2s) ay = (Coo-C33)/(Cop + C33) (2d) ion De) | = 2Cp3/(Cop + C33) (2e) where C,, is the coincident spectrum of an auto spectrum Ca; is the coincident spectrum of a cross spectrum al refers to heave 2 refers to north-south slope and 3 refers to east-west slope The first coefficient, aq » is the wave energy spectral density. The mean direction the waves are coming from is defined by ine -1( T = tan b,/a,) (3) The significant wave height and significant period are defined as, (B05 (my) 12 (4) ye tal aes (5) where m, is the nth moment of the spectral density m = f S,(f) £ af (6) 10) A more detailed discussion on the analysis can be found in Reference 17. The RMS spreading angle for a narrow banded sea can be determined by: /; L 2 2y1Ya) 12 (7) Os Sra Alene HS DATA PROCESSING The Wave-Track data was passed through a two hertz low pass filter and digi- tized at four samples per second per channel. The tape speed was set at 3-3/4 ips. This is equivalent to an actual sample rate of two hertz with a low pass filter cutoff at one hertz. The engineering units are applied to the data, while the data in the direction channels are converted from tilt angles to slopes. When necessary, the data were filtered using a two-pole high pass filter to eliminate electronic drifts or offsets. The auto and cross spectra were calculated using a Fast Fourier Transformation (FFT). The data runs were divided into segments, each of a size based on the power of two. A cosine window was applied to each segment and the segments are overlapped by 50 percent. The real and the imaginary parts of the cross spectra of each of the three channels were calculated to give the coincident and the quadrature spectra. From these, the Fourier coefficients were calculated, along with the directions, periods, and energies. Typical lengths of a run are 1728 and 1600 seconds with the number of degrees of freedom of 51 and 47, respectively. DISCUSSION The data presented here represent two different approaches to measuring waves and their directions from a ship launched buoy. Delft University analyzed the WAVEC data and reported them in Reference 9. DTNSRDC analyzed the Wave-Track data. The displayed results for a comparison of the two buoys include time histories of significant wave height, modal wave period, and mean wave directions. In the graph of the time histories, the mean wave direction is defined by the frequency band containing the greatest energy. Also included, are energy spectral densities, mean wave directions, and RMS spreading angles measured by both buoys for most of the runs. The bulk of the runs were made between 14 May and 18 May 1982, with only one run each made on the 17th, 19th, 20th, and 2lst. The date, time, and location for each run can be found in Table 1. The relationship between the wind speed and direction and the significant wave height, modal wave period and mean wave directions can be seen in Figures 6 and 7. Continuous time histories are displayed, but not every run was plotted. The runs not included can be found in Table l. The energy densities, mean wave directions, and spreading angles for the two buoys are presented in Figures 8 through 23. Tables of values for these three categories from Delft University were not available to the authors, so the graphic results were used. Scales were matched and the results of the Wave-Track buoy data were overlaid on the WAVEC buoy data. The frequency range used in the DTNSRDC ana- lysis is 0.047 hertz to 0.30 hertz. The Dutch analysis, performed by the Department of Hydro-Instrumentation (DHI) of the Ministry of Public Works in the Netherlands, uses a range of 0.05 to 0.50 hertz. The displayed frequency range has been limited to 0.4 hertz. On the 14th of May, the significant wave height started out as measured at 1.5 meters. It slowly decreased by the last measurement of the day in accordance with a generally decreasing wind speed coming from a steady direction of 170 degrees. The modal wave period remained fairly steady at about seven seconds. On the 15th, the wind was fairly steady, still blowing in from 160 to 170 degrees. The wind speed remained fairly strong in the neighborhood of 12 meters per second until shortly after 1800 GMT, when the wind dropped off and the direc- tion shifted 90 degrees to the west. The significant wave height increased steadily in accordance with the increased wind speed and steady direction. The modal period started a little lower than it had ended on the 14th, but increased to and hovered around eight seconds. This also is as expected with the stronger wind than the previous day, for a steady direction. The measurements were made in the same general area on the 1th and the 15th, as seen in Figure 5. On the 16th of May, the ship was west of the previous area (see Figure 5). During the measurements, the wind direction slowly shifted westerly to 210 degrees, as the wind speed decreased. At the start of measurements on this day, the signi- ficant wave height is about half a meter less than that ending the previous day and the modal wave period is one to two seconds longer. The lower wave heights and longer periods indicate a decaying swell condition and is born out by the lower measured wind speed and change in direction. This shift into the swell range can also be seen in the spectra of runs 26 through 28 (Figures 17 and 18). A single wind measurement on the 17th indicated a low speed and a direction out of 300 degrees. On this day, a maximum modal period was reached for each buoy and a local minimum significant wave height was measured. The 18th was the last day that several measurements were recorded in suc- cession. After an initial drop in wind speed, the speed increased to a maximum during run 35, before dropping off. During this time, the wind shifted from about 150 to 215 degrees. The significant wave height measurement slightly increased and decreased with the wind speed, while the modal wave period decreased. This indi- cates an increase in wind wave energy accompanying a slowly decaying swell. The last three runs were made on separate days at different locations. Throughout the trial, the total energies measured by both buoys are very close, as indicated by the significant wave heights. The mean and RMS values of the percent differences of the two buoys are 0.32 percent and 6.7 percent, respectively. The modal wave periods are also quite close, with a couple of exceptions, until the end of the 15th of May. However, from the 16th until the 21st, the WAVEC buoy measured a larger modal period than the Wave-Track buoy. The mean and RMS values of the percent differences are 4.5 percent and 7.0 percent, respectively. As mentioned earlier, the wind direction is steady, around 170 degrees, from Run 3 to Run 24. The observed wave directions on the l4th are coming from 200 degrees. On the 15th, the observed wave direction is more closely in line with the measured wind direction. The directions differ by about 20 degrees near the beginning of the day and then close to the same direction towards the end of the day before the wind shifts direction. On the 16th, at location four, the observed wave direction is back to 200 degrees. On the 18th, at location six, the direction that the waves were observed to be coming from was 330 degrees. The direction that the waves were observed to be coming from agreed more closely with the mean direction of the dominant frequency for the Wave-Track near the beginning of the trial and more closely with the WAVEC toward the end of the trial.* On the 14th the observed wave direction agreed quite well with the mean wave direction of the dominant frequency as measured by the Wave-Track. On the 15th, the Wave-Track buoy's indicated mean direction of the dominant frequency con- tinued to vary about the mean value of 200 degrees, while the observed direction shifted to 165 to 180 degrees. The mean wave direction of the dominant frequency for the Wave-Track buoy on the 18th, varied significantly from run to run. While recording the data for Run 35, it was noticed that the signals from the direction channels had drifted out of the linear recording range of the analog tape recorder. The direction channels coming out of the receiver were then zeroed, but a few pre- vious runs may also have been affected. ; The directions measured by the WAVEC and Wave-Track buoys differ throughout the trial. However, shifts of the mean wave directions of the dominant frequency between the two buoys generally agree in time and in the direction of the shift. This may indicate a relative offset between the two buoys! magnetic recordings or coordinate resolution. The energy densities, as measured by both buoys, agree well, with a few minor exceptions. The spectral shapes are similar, but in several cases the density peaks of the WAVEC data are noticeably greater than the Wave-Track data. The data analyzed by DHI produced a greater frequency resolution than for the Wave-Track buoy data analyzed by DINSRDC. The data from the WAVEC buoy shows higher, sharper peaks while the Wave-Track buoy data shows broader peaks. When two or more sharp peaks close together are produced by the analysis with greater resolution, the other analysis may combine them into one or two shorter broad peaks. Overall the total energy measured by both buoys is about the same for each run. As mentioned earlier, the data segments in the DTNSRDC analysis are overlapped by 50 percent to smooth the results. The DHI analysis averages the spectral den- sities in 0.05 hertz bandwidth for each frequency center. Confidence limits are generally narrower when less resolution is required, given similar data lengths and sample rates. The mean wave directions between the two buoys generally agree for frequencies above 0.11 hertz. A correction for the magnetic declination of 13 degrees west has been applied to the mean directions of the Wave-Track buoy data. This may account *The direction of the dominant frequency is likely to be the direction most easily observed. 10 for some of the differences at the frequencies above 0.11 hertz. The Wave-Track results show a problem in defining directions in the lower frequency range. The extent of the frequency range for this problem seems to vary from run to run. The authors believe this is due to the hydrodynamic phase lag reflected primarily in the tilt channels. This lag may be greater for the longer waves that have a smaller orbital differential over the depth of the buoy than for shorter waves. The spreading angles of the directional waves for the buoys can be seen in the lower graph of these figures. The spreading for the Wave-Track buoy data is con- sistently high in the lower frequency range, including the peak frequency at times. The spreading then drops to a lower level, still above that for the WAVEC data, in the middle frequencies. Finally, the spreading increases in the upper frequencies. A reasonable amount of spreading occurs in a range around the peak frequency for the WAVEC buoy data. Different spreading functions were used to calculate WAVEC and Wave-Track spreading angles. The high level of spreading in the lower frequencies of the Wave-Track data may be due to the buoy's response to non-unidirectional orbital velocities in the long 18 waves. Forrestal, et al. noted a complicated flow field in a large wave during Hurricane Delia. Three current meters were strung in the water column. The upper current meter measured the greatest horizontal velocities to be in the east-west direction; however, the velocities in the north-south direction were not negli- gible. The velocities can flow in a horizontally eliptical manner, and so the corresponding movement of the buoy stem can be in an eliptical manner, rather than linearly unidirectional. This trial provided two opportunities to measure changing sea conditions over periods of several hours. In the first case, for Runs 10-25, wave data were measured from 0820 to 1843 on 15 May 1982. Middle frequency waves were coming out of the west (250-270 degrees) throughout the day, while some higher frequency wind driven waves were coming from the south (180-190 degrees). As the day progressed, the energy in the mid frequencies generally increased, with some fluctuations, until the last run. The energy in the waves that were closely aligned with the wind, i.e., south, continued to increase, with a corresponding increase in period. This can also be seen in the directions, as the ramp between the west and the south shifts to the left and becomes less steep. This is more clearly seen in the mean directions of WAVEC data than the Wave-Track data. alia In the second case, a distinct development of bimodal seas can be seen. This occurred for Runs 31 to 36 from 0755 to 1340 on 18 May 1982. A generally decaying swell came from north-northwest (330-350 degrees). Over the same period of time, wind driven waves grew as they came from the south (180 degrees). The energy in the wind waves continued to grow and the period increased, until they ultimately approached and surpassed the swell energy in Run 36. The increasing period of the wind waves can also be seen in the graphs of mean directions, as the waves from the south begin to shift to the middle frequency range. CONCLUDING REMARKS Throughout the trial the wave measurements of the WAVEC and Wave-Track buoys agree in energy and modal period. There is a slightly greater difference between the modal wave periods than the significant wave heights, as measured by the two buoys. The measurements of the mean wave direction, associated with the modal period, were fairly consistent between the two buoys. However, there was an offset between the two, possibly due to magnetic influences or difficulties in an elec-— tronic coordinate resolution. The spectral densities, mean directions, and spreading angles are also presented for the two directional sensing wave buoys for most of the runs. The spectral density distributions of the two buoys agreed well in most cases. The agreement was not as clear, however, for the mean directions. The middle and upper frequency directions generally agreed, but the lower frequency directions measured by the Wave-Track buoy changed too much. The spreading of wave energy, aS measured by the WAVEC buoy, was less than that for the Wave-Track buoy. This may be due in part to a side effect orbital wave velocities have on the sub- mersed stem of the Wave-Track buoy. Two cases of changing wave conditions were also measured. In one case, two growing wave systems from different directions combined to a common frequency range. The system aligned with the wind grew more quickly. In the other case, a distinct bimodal wave system was evident. The swell from one direction slowly degraded, while the wind driven sea from another direction increased in energy and period. While the Delft buoy was also used to gather wave data, the results are not included here. The authors did not have access to the raw data, and the results available were calculated using a different method than for the results presented here for the other two buoys. 12 Another comparison of directional wave measuring systems is scheduled to take place during a sea trial in March 1987. A multinational effort will be carried out under the auspices of Research Study Group (RSG)1, Full Scale Wave Measurements, chaired by the U.S.A., under Special Group of Experts on Hydrodynamics (AC/243 (Hydro)). The Dutch research ship TYDEMAN and the Canadian research ship QUEST will be used as launching platforms. This upcoming trial will bring together an interesting variety of in-situ directional wave measurement systems, including buoys and possibly shipboard radar. A comparison of SOWM forecasts and buoy measurements during the TYDEMAN trial is the subject of a future publication. Also included will be comparisons of SOWM forecasts and wave measurements conducted during other sea trials. ACKNOWLEDGMENTS The kind cooperation of the Royal Netherlands Navy, Exchange Agreement No. MWDDEA N-65-TN-4803, allowed this sea trial to be carried out. Dr. ir. J.M. Dirkzwager of the Ministry of Defence is gratefully acknowledged for his coor- dination in arranging the trial. The Delft University team headed by Prof. ier. J. Gerritsma contributed greatly to the technical success of the trial. The assistance of Messrs. M. Buitenhek and J. Ooms is greatly appreciated as is the assistance of Mr. Gerritsen of Datawell. The officers and crew of the TYDEMAN, under the able leadership of CAPT A.P.H.M. Lempers, are gratefully acknowledged, for their assistance throughout the trial. The coordination of the American efforts by Ms. S.L. Bales of DINSRDC is greatly appreciated. The wave forecasts radioed by FNOC were quite helpful in planning the ship's route and the efforts of LCDR Mass are particularly appreciated. The assistance by Ms. C. Bennet and ENS's G. Hobson and A. Meurer of DINSRDC has been very helpful. 13 REFERENCES 1. lLazanoff, S.M. and N.M. Stevenson, "An Evaluation of a Hemispheric Operational Wave Spectral Model," FNWC Technical Note 75-3 (Jul 1975). 2. Cummins, W.E. and S.L. Bales, "Extreme Value and Rare Occurrence Wave Statistics for Northern Hemisphere Shipping Lanes," Proceedings of the Society of Naval Architects and Marine Engineers STAR Symposium (Jun 1980). 3. Bales, S.L., W.T. Lee and J.M. Voelker, "Standardized Wave and Wind Environments for NATO Operational Areas," Report DINSRDC/SPD-0919-01 (Jul 1981). 4, Cummins, W.E., S.L. Bales and D.M. Gentile, "Hindcasting Waves for Engineering Applications," Proceedings of the International Symposium on Hydrodynamics in Ocean Engineering, The Norwegian Institute of Technology (Aug 1981). 5. Bales, S.L., WeE. Cummins and E.N. Comstock, "Potential Impact of Twenty Year Hindcast Wind and Wave Climatology on ship Design," Marine Technology, Vol. 19, No. 2 (Apr 1982). 6. Bales, S.L., "Designing Ships to the Natural Environment," Naval Engineering Journal, Vol. 95, No. 2 (Mar 1983). 7. "U.S. Navy Hindcast Spectral Ocean Wave Model Climatic Atlas: North Atlantic Ocean," prepared by Naval Oceanography Command Detachment, Asheville, North Carolina (Oct 1983). 8. Foley, E.W., ReJ. Bachman and S.L. Bales, "Open Ocean Wave Buoy Comparisons in the North Atlantic," Proceedings 1983 Symposium on Buoy Technology (Apr 1983). 9..Gerritsma, J., "Wave and Ship Motion Measurements Hr. Ms. TYDEMAN Trials 1982," Delft University of Technology, Report No. 593 (Jul 1983). 10. Gerritsma, J., "Results of Recent Full Scale Seakeeping Trials," Technische Hogeschool Delft, Laboratorium Voor Scheepshydromechanica, Report No. hO5 (Mar 1980). @ 11. Buitenhek, M. and J. Ooms, "An Updated Design of a Disposable Wave Buoy," Technische Hogeschool Delft, Report No. 463 (May 1978). 12. Middleton, F.H., LR. LeBlanc and M. Czarnecki, "Spectral Turning and Calibration of a Wave Follower Buoy," Eighth Annual Offshore Technology Conference, Paper No. OTC 2597 (May 1976). 15 13. Middleton, F.H., L.R. LeBlanc and W. Sternberger, "Wave Direction Measurement by a Single Wave Follower Buoy," Tenth Annual Offshore Technology Conference, paper No. OTC 3180 (May 1978). 14. Brainard, E.C., "Wave Orbital Following Buoy," Paper presented at Marine Technology '80 Conference (not in the transactions) (Oct 1980). 15. LeBlanc, L.R. and F.H. Middleton, "Storm Directional Wave Spectra Measured with a Single Buoy," Oceans '82 Conference (Sep 1982). 16. Ewing, J.A. and E.G. Pitt, "Measurements of the Directional Wave Spectrum off South List," Conference on Wave and Wind Directionality: Applications to the Design of Structures, Paris (1982). 17. Lai, R.J. and R.J. Bachman, "Directional Wave Measurement and Analysis," Report DINSRDC/SPD-1167-01 (Sep 1985). 18. Forristall, G.Z. et al., "The Directional Spectra and Kinematics of Surface Gravity Waves in Tropical Storm Delia," Journal of Physical Oceanography , Vol. 8, No. 5 (Sep 1978). 16 TTemegeq - 1 OINST 4 84 cm — STABILIZATION WEIGHT (13kg) Figure 2 - Delft Disposable Buoy 18 Figure 3 - Stabilization of Delft Buoy 9 76 cm 184 cm Figure 4 —- ENDECO Type 956 Wave-Track Buoy 20 Figure 5 — TYDEMAN Transit Route eal Ov uOTIIeATG SAPM PeATESGQ pue sUOTIIeITG aAeM pernsedW SUOCTIDeATG ‘peeds putTM jo AAOISTH OWT] - 9 oAn8Ty qg ean3T 4 Y3eINNN NNY _ 9 v6 26.0 8% 9% ve @ 02 81 92 wb 2 ob 8s; 9 v 2 Oy oo Te oe — oo ° ° ° ——— 6 6 GNIM ec ceece G3aAuSSEO —- —— OO3GN3 JAVA = — — eQ JINSTA Ol St 02e (Gap) SNOLLOSUIG NVAW (sdw) GNIM 22 Ov 8E WYSToH sAeM JUeDTJTUSTS pue poTAdg DAeM TeEpoW FO AAORSTYH OUTL - / san3tTy qi ean3t A YaGINNN NOY 96 ve ze Of 8 9% ve 2 OF Bt OF ve 2 oO 8 e/ ean3ty OOSGNSA JJAVM —-—— (suaj}aW) LHOISH SAVM LNWOISINDIS (998) GOldad 1WGON RUN 3 RUN 4 3.0 3.0 3 o ——ENDECO BUOY 0 2.5 & 2.5-— --—-WAVEC BUOY I ] nN | E 2.0 E 2.0 s z H 1.5 @ 1.5 z zZ Ww WwW Oo 1:0 2 1.0 a > o GC} wi 0.5 = 0.5 = 2 uw TT] 0.9 — 0.01 0.0 0.14 O02 O03 0.4 0.0 O14 O2 O03 0.4 FREQUENCY (hz) FREQUENCY (hz) 360 i) =~ 3 Ey > 270 = 2a ° ro) fe - Oo oO cr 180 ul a ran) z z < < Lu ul 90 ul 0 0 | 0.0 01 O02 O83 0.4 0.0 O14 O2 O38 0.4 FREQUENCY (hz) FREQUENCY (hz) 90 - 90 —J rs) -_ te) & 60 2 60 2 S (a) — < a oo wi co a 30 7 30 o wo 0 0! 0.0 O14 O2 O83 0.4 0.0 O04 O2 O3 0.4 FREQUENCY (hz) FREQUENCY (hz) Figure 8 - Energy Densities, Mean Directions, and Spreading for Runs 3 and 4 eh RUN 5 RUN 6 oe 3.0 ® 8 —— ENDECO BUOY @ 2.5)— --— WAVEC BUOY ‘E na = E 2.0 s fe 4 D 1.5 Ww TT a ra) = 1.0 > o Oo x ra Lu wi 0.5 = 2 uy i 0.90 L-® 0.0 01 O02 O38 0.4 0.0 01 O02 O03 0.4 FREQUENCY (hz) FREQUENCY (hz) 360 360 i be 3S 270 S 270 za 5 S = E & 180 © 180 cc oc ra a Z 90 Z 90 ve Ww S s 0 0 alo On Olan Ors 014 0.0 O14 O02 O03 0.4 FREQUENCY (hz) FREQUENCY (hz) 90 90 i) 7) 3 60 s 60 o) Oo Zz Zz 3 a i ‘ a 30 < 30 (7p) (7p) 0 0 0.0 01 O02 O03 0.4 0.0 0.1 02 O03 04 FREQUENCY (hz) FREQUENCY (hz) Figure 9 - Energy Densities, Mean Directions, and Spreading for Runs 5 and 6 2 RUN 7 3.0 RUN 8 g 3 —— ENDECO BUOY if --=- WAVEC BUOY AN ; — > fe s nH (7) a a ia 2 S > 5 fe Cr ui w 2 Ww WwW 01 02 03 0.4 0.1 02 03 0.4 FREQUENCY (hz) FREQUENCY (hz) 360 360 3 B 3 270 5 270 a o S © 180 & 180 4 Ww 2 cc (a) Ta) 2 90 Zz 90 Ww wi = Ss : 0 0.1 02 03 0.4 01 02 03 0.4 FREQUENCY (hz) FREQUENCY (hz) 90 B ~ 3 Ss 60 2 g (a) = a : 5 a. © 30 % o 0.0 041 02 O03 0.4 0.0 01 02 0.3 FREQUENCY (hz) FREQUENCY (hz) Figure 10 - Energy Densities, Mean Directions, and Spreading for Runs 7 and 8 26 RUN 9 RUN 10 3.0 Py) ry —— ENDECO BUOY ® 2.5 Bs --- WAVEC BUOY a N E 20 E Z i D 1.5 2 Ww rt) O 1.0 o > > Sg f i 0.5 wi in i 0.0 0 0.0 0.14 O02 O03 0.4 0.0 0.4 0.2 O38 0.4 FREQUENCY (hz) FREQUENCY (hz) 360 2) 2) S 270 3 Zz 5 S e - O 180 O oc oc ra a = 90 z WW Lu Ss Ss 0 0 0.0 0.1 O02 O03 0.4 0.0 014 O2 O03 0.4 FREQUENCY (hz) FREQUENCY (hz) SPREADING (deg) SPREADING (deg) 00 O01 O02 03 0.4 0.0 O01 O02 O3 0.4 FREQUENCY (hz) FREQUENCY (hz) Figure 11 - Energy Densities, Mean Directions, and Spreading for Runs 9 and 10 eT RUN 12 0.4 RUN 14 -—— ENDECO BUOY ---WAVEC BUOY ENERGY DENSITY (m?-sec) & (=) ENERGY DENSITY (m?- sec) 0.0 -—As 7 : 0.0 0.1 0.2 O33 0.4 0.0 0.1 02 #03 0.4 FREQUENCY (hz) FREQUENCY (hz) B 2) ® ® as oS 2 4 2} o oe - Oo oO Ww Ww cc cc ia) [a 2 r-4 << G 1.0 6 2.0] a o = WwW nT p a 0.0 0.0 bs 0.0 01 O02 O03 0.4 0.0 0.1 0.2 03 0.4 FREQUENCY (hz) FREQUENCY (hz) 360 360 3 Ey 3 270 3 270 Zz S S E - © 180 © 180 uw Lu a ES ra) a 2 = 90 =< 90 Ww uu = = 0 0 OfOM 0! 102 0!ataatol4 0.0 O14 0.2 0.3 0.4 FREQUENCY (hz) FREQUENCY (hz) 90 S B g S 60 (a) < mr ig a 30 a e 77) 0 0 : 0.0 FxOnl WiOl2 ) 10.34 0.4 0.0 0.1 O02 O38 0.4 FREQUENCY (hz) FREQUENCY (hz) Figure 13 - Energy Densities, Mean Directions, and Spreading for Runs 16 and 17 2g RUN 19 ___RUN 20 6.0 6.0 8 : —— ENDECO BUOY 5.0 a | WAVEC BUOY - N N = 40 E > > F E B 3.0 G = Ae re 8 = we ~=6+21.0 wi 2a a Ww uy 0.0 ol2 0.0 01 O02 O38 0.4 0.0 O01 O02 O03 0.4 FREQUENCY (hz) FREQUENCY (hz) 360 360 = ro.) te) @ ® S 270 = 270 za Q 2 5 oO wu 180 = 180 5 5 z 90 < 90 = S 0 0 0'0) Osmo! 20'S) "014 Og Oa OT" (OL FREQUENCY (hz) FREQUENCY (hz) 90 ' B _ ® 3 60 3 J ie eo) S | = Z fa) | i < | uu cc LiSO Hh a. O. 7p) oO \ 0 0 0:00: 1nn0:2°aO Ss imNOl4 O\OMMONpnto'20) O13 Sola FREQUENCY (hz) FREQUENCY (hz) Figure 14 - Energy Densities, Mean Directions, and Spreading for Runs 19 and 20 30 RUN 21 RUN 22 8.0 i] — 6.0 3 z f Hm 4.0 ” a ry a [a) > 5 2.0 G} ce a Ww WwW za za Ww 0.0 Os "0.0 0.1 O2 O3 0.4 0.0 O14 O02 O23 0.4 FREQUENCY (hz) FREQUENCY (hz) 360 360 S 270 3 270 z z fe) ° e Ee © 180 © 180 oc cc a ran) za za 90 < < 90 s s 0 0 | 0.0 O14 O2 O38 0.4 0.0 O14 O02 O38 0.4 FREQUENCY (hz) FREQUENCY (hz) 90 90 ; —— ENDECO BUOY] -- WAVEC BUOY |} Se r.) q 60 s 60 O Q < rf © 30 © 30 a a 7) ” 0 QO! —_ 0.0 O14 O02 O38 04 0.0 0.1 0.2 O38 0.4 FREQUENCY (hz) FREQUENCY (hz) Figure 15 - Energy Densities, Mean Directions, and Spreading for Runs 21 and 22 Si RUN 23 ____ RUN 24 8.0 8.0 o S —— ENDECO BUOY rd o --- WAVEC BUOY I 1 3 6.0 * i 2 “” 4.0 7) ci vi a a = > 2 2.0 Oo wi ec WW in 2 | 0.0 0.0 0.1 O02 0.3 0.4 0.0 0.1 O02 O03 0.4 FREQUENCY (hz) FREQUENCY (hz) 360 360 2) Fo.) S 270 S 270 2a S S - = © 180 O 180 cc or ra ra Z 90 4 90 = = 0 0 0.0 0.1 O02 O03 0.4 OO Of SO OF Oy FREQUENCY (hz) FREQUENCY (hz) SPREADING (deg) SPREADING (deg) OO CAO RE OS AOn O10) WOM oe ors) lola FREQUENCY (hz) FREQUENCY (hz) Figure 16 - Energy Densities, Mean Directions, and Spreading for Runs 23 and 24 32 RUN 25 RUN 26 6.0 6.0 o o @ @ 5.0 & 5.0 N Nn E 40 E 4.0 s Z 2 3.0 D 3.0 = Ww = 20 QO 2.0 > = oO uj 1.0 f 4.0 fry : i 0.0 0.0 0.0 0.14 02 03 0.4 0.0 0.4 O02 O03 0.4 FREQUENCY (hz) FREQUENCY (hz) 360 360 3 si 3 270 S 270 = 6 5 = - © 180 9 180 Ww ia c a ray a Z 90 < 90 Ww WwW) Ss = 0 0 0.0 01 O02 O03 04 0.0 O01 O02 O38 0.4 FREQUENCY (hz) FREQUENCY (hz) 90 90 f-)) B g 60 a, 60 (O} [O) z = Q Qa xt 4 uu Li 30 & 30 i?2) i?p) ENDECO BUOY === = WAVEC BUOY 0 0 | paced 0.0 014 O02 O38 0.4 0.0 0.4 O02 O38 0.4 FREQUENCY (hz) FREQUENCY (hz) Figure 17 - Energy Densities, Mean Directions, and Spreading for Runs 25 and 26 33 RUN 27 RUN 28 4.0 6.0 Co oe @ @ =—— ENDECO BUOY | I -== WAVEC BUOY B 3.0 B > > = = Q 2.0 2 uw Ww Qa Qa > > S 1.0 S Ww uw Zz Zz Ww Ww 0.0 = y 0.0 0.1 0.2 6.3 0.4 0.0 0.1 0.2 0.3 0.4 FREQUENCY (hz) 360 90 MEAN DIRECTION (deg) MEAN DIRECTION (deg) oo (=) 0 — 0 OOM Oni m0! omOS Ola OOM OM OL2hw lols" oa FREQUENCY (hz) FREQUENCY (hz) 90 = = Ss 60 3 Oo (0) 2 2 Qa [=] 6 C c [ug 5 = a a ONG 0.1 02 O38 0.4 "0.0 0.1 O02 03 04 FREQUENCY (hz) FREQUENCY (hz) 360 360 DB = s i | ~— 270 3B 270 za 2 5 & = Ww 180 O 180 : : a 90 = 90 Ww c-¢ = = 0 0 0.0 01 O02 O03 0.4 DOO SIMO! OIL LO a mnOL4 FREQUENCY (hz) FREQUENCY (hz) 90 a B Sy o J 3 60 G} G} = 2 [a) < a en c a a 30 ” (¢p) —— ENDECO BUOY ----— WAVEC BUOY 0 0 0.0 0.1 O02 O03 0.4 OOMEOSILO nn 0 Sioa FREQUENCY (hz) FREQUENCY (hz) Figure 19 - Energy Densities, Mean Directions, and Spreading for Runs 30 and 31 35 ss (=) > > —= So og 2 a2 oe 2) Oy rf S ow az Zl a= o Ww >| s< 2 c| fe iS) ee | ot ! S o 6 9° 920 9 8 COL CO ee et Ne (98s - ,w) ALISNAG ADYANA 4 0.3 RUN 32 0.2 FREQUENCY (hz) 0.1 SS 6, .6. so 2. 9° On = Oe Ne =O (98s - ,wW) ALISNAG ADYANA (629p) NOILLOSHIG NV3IN (6ap) NOILOSHIG NV3IN 0.4 0.3 0.2 FREQUENCY (hz) 0.1 0.0 FREQUENCY (hz) (Sep) SNIGWSYdS 0.2 0.0 0.1 FREQUENCY (hz) FREQUENCY (hz) Figure 20 - Energy Densities, Mean Directions, and Spreading for Runs 32 and 33 36 RUN 34 RUN 35 ~ 6.0 6.0 oO =~ ® (S) ? 2 E * > 4.0 > (2) = ai 3.0 2 = 20 e eo C 2 5 2 1.0 2 0.0 a f Me 0.0 O01 O02 O03 0.4 0.0 O01 O02 O03 0.4 FREQUENCY (hz) FREQUENCY (hz) 360 DS 3S S £ 270 = So 5 = = 0 © 180 lu a (wa S a 4 2 90 ul < = s 0 0 0.0 01 02 O03 0.4 0.0 01 O02 03 04 FREQUENCY (hz) FREQUENCY (hz) 90 90 i) ir) g 60 g 60 6 6 Zz Zz (a) Qa c~¢ 1.0 > © © : : 7 as = uJ uJ 0.0 0.0 01 02 O03 0.4 OO OP) CO FREQUENCY (hz) FREQUENCY (hz) 360 360 B @ 3 270 3 270 r4 : : © 180 | G 180 a [a) z za Z 90 z 90 uJ Ss = 0 0 : : : OOO | Om OS) WL O!ON MOMmmO-omNora) 014 FREQUENCY (hz) FREQUENCY (hz) BS @ o zo = O O < z 2 [=) < cr a a. oe 7 a 7p) 0 0 O10" Vor So:2aro's ova O10 MOnMMOGLoninlOrs Ola FREQUENCY (hz) FREQUENCY (hz) Figure 22 - Energy Densities, Mean Directions, and Spreading for Runs 36 and 38 38 RUN 39 2.0 1.5 1.0 0.5 ENERGY DENSITY (m2 -sec) 0.0 - : 0.0 074 O02 O83 0.4 FREQUENCY (hz) 360 270 90 MEAN DIRECTION (deg) © (=) 0 0.0 0.1 0.2 03 0.4 FREQUENCY (hz) 90 60 30 SPREADING (deg) — ENDECO BUOY --- WAVEC BUOY 0 0.0 Of O02 03 #40.4 FREQUENCY (hz) Figure 23 - Energy Density, Mean Direction, and Spreading for Run 39 39 TABLE 1 - TIMES AND LOCATIONS OF DATA COLLECTION Time Latitude Longitude Run Date GMT Location (deg N) (deg W) 1511-1555 1600-1631 1639-1709 1715-1745 1752-1820 1828-1857 1906-1935 0820-0851 0930-1000 1012-102 1100-1130 1238-1309 1320-1350 1356-1426 1553-1623 1628-1658 1702-1732 1738-1802 1813-1843 0912-092 0954-1034 1130-1200 0748-0818 0755-0825 0830-0900 0922-0952 0959-1029 1058-1128 1212-122 1240-1337 Telos iano 1249-1319 OMDNLENDNNNDNDAANAAUW I! FFEFWWWWWWwl Wwlwiwl wnnnnnwn hr WWW EEF ErWW LO DTNSRDC ISSUES THREE TYPES OF REPORTS 1. DTNSRDC REPORTS, A FORMAL SERIES, CONTAIN INFORMATION OF PERMANENT TECH- NICAL VALUE. THEY CARRY A CONSECUTIVE NUMERICAL IDENTIFICATION REGARDLESS OF THEIR CLASSIFICATION OR THE ORIGINATING DEPARTMENT. 2. DEPARTMENTAL REPORTS, A SEMIFORMAL SERIES, CONTAIN INFORMATION OF A PRELIM- INARY, TEMPORARY, OR PROPRIETARY NATURE OR OF LIMITED INTEREST OR SIGNIFICANCE. THEY CARRY A DEPARTMENTAL ALPHANUMERICAL IDENTIFICATION. 3. TECHNICAL MEMORANDA, AN INFORMAL SERIES, CONTAIN TECHNICAL DOCUMENTATION OF LIMITED USE AND INTEREST. THEY ARE PRIMARILY WORKING PAPERS INTENDED FOR IN- TERNAL USE. THEY CARRY AN IDENTIFYING NUMBER WHICH INDICATES THEIR TYPE AND THE NUMERICAL CODE OF THE ORIGINATING DEPARTMENT. ANY DISTRIBUTION OUTSIDE DTNSRDC MUST BE APPROVED BY THE HEAD OF THE ORIGINATING DEPARTMENT ON A CASE-BY-CASE BASIS. ———<——— ee = DOCUMENT LIBRARY Woods Hole Oceanographic Institution JUN 12 1986 oar